JP6856972B2 - Lithium-ion secondary battery electrode slurry composition, lithium-ion secondary battery negative electrode and lithium-ion secondary battery - Google Patents

Description

The present invention relates to a slurry composition for a lithium ion secondary battery electrode, a negative electrode of a lithium ion secondary battery, and a lithium ion secondary battery.

In recent years, mobile terminals such as mobile phones, notebook computers, and pad-type information terminal devices have become remarkably widespread. Lithium-ion secondary batteries are often used as the secondary batteries used as the power source for these mobile terminals. Since mobile terminals are required to be more comfortable to carry, they are rapidly becoming smaller, thinner, lighter, and higher in performance, and are now used in various places. This trend is still ongoing, and batteries used in mobile terminals are also required to be smaller, thinner, lighter, and have higher performance.

In a lithium ion secondary battery, a positive electrode and a negative electrode are installed via a separator, and _{lithium such as LiPF 6} , LiBF ₄ LiTFSI (lithium (bistrifluoromethylsulfonylimide)) and LiFSI (lithium (bisfluorosulfonylimide)) is used. It has a structure in which a salt is stored in a container together with an electrolytic solution in which a salt is dissolved in an organic liquid such as ethylene carbonate.

The negative electrode and the positive electrode are usually obtained by dissolving or dispersing a binder and a thickener in water, and mixing the active material and, if necessary, a conductive auxiliary agent (conducting agent) with the slurry for electrodes (conductivity-imparting agent). Hereinafter, it may be simply referred to as slurry) is applied to the current collector, and the water is dried to form a mixed layer. More specifically, for example, in the negative electrode, a carbonaceous material capable of occluding and releasing lithium ions as an active material and, if necessary, a conductive auxiliary agent such as acetylene black are used as a secondary to a current collector such as copper. They are bound to each other by a binder for battery electrodes. On the other hand, in the positive electrode, LiCoO ₂ , which is an active material, and, if necessary, a conductive auxiliary agent similar to that of the negative electrode are bound to each other in a current collector such as aluminum using a binder for a secondary battery electrode. It is a thing.

So far, diene-based rubbers such as styrene-butadiene rubber and acrylic-based binders such as polyacrylic acid have been used as binders for aqueous media (for example, Patent Documents 1 and 2). Examples of the thickener include methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropoxy cellulose, carboxymethyl cellulose sodium salt (CMC-Na), sodium polyacrylic acid and the like, and CMC-Na is often used among them. (For example, Patent Document 3).

However, diene-based rubber such as styrene-butadiene rubber has a problem that the adhesiveness to the metal collecting electrode such as copper is low, and the amount used cannot be reduced in order to improve the adhesion between the collecting electrode and the electrode material. .. Another problem is that it is vulnerable to heat generated during charging and discharging and has a low capacity retention rate. Recently, there have been increasing demands for extending the usage time of mobile terminals and shortening the charging time, and there is an urgent need to improve battery capacity (lower resistance), life (cycle characteristics), and charging speed (rate characteristics). Among them, it is a particular obstacle.

In a lithium ion secondary battery, the battery capacity is affected by the amount of active material. Therefore, in order to increase the active material in the limited space of the battery, the amount of binder and thickener in the electrode slurry should be suppressed. Is valid. Further, since the rate characteristics are also affected by the ease of electron movement, it is effective to suppress the amount of the binder and the thickener which are non-conductive and hinder the movement of electrons. However, if the amount of the binder and the thickener is reduced, the binding property between the collecting electrode and the electrode material and the active material in the electrode is lowered, and the durability (battery life) for long-term use is only significantly lowered. Instead, it becomes brittle as an electrode. As described above, until now, it has been difficult to improve the battery characteristics such as the battery capacity while maintaining the bondability between the collecting electrode and the electrode material.

Japanese Unexamined Patent Publication No. 2000-67717 Japanese Unexamined Patent Publication No. 2008-288214 Japanese Unexamined Patent Publication No. 2014-13693

The present invention has been made in view of the above problems, and an object of the present invention is to improve the battery characteristics of the electrode slurry without impairing the adhesiveness with the current collector foil and the bondability with the active material. And.

As a result of diligent research to solve the above problems, the present inventors have found that the above object can be achieved by using a slurry composition for a lithium ion secondary battery electrode having the following configuration, and based on this finding, further The present invention was completed through repeated studies.

That is, the slurry composition for a lithium ion secondary battery electrode (hereinafter, also simply referred to as a slurry composition) according to one aspect of the present invention includes α-olefin-maleic acids obtained by copolymerizing α-olefins and maleic acids. A slurry composition for a lithium ion secondary battery electrode composed of a binder composition containing a neutralizing salt of a polymer, a conductive auxiliary agent, a negative electrode active material, and water, when the solid content concentration is 50% by weight. It is characterized in that the viscosity at 25 ° C. and a shear rate of 100 s- ¹ is 400 mPa · s-10000 mPa · s.

It is considered that such a configuration can improve the battery characteristics without impairing the binding property of the electrode slurry.

In the slurry composition, when the solid content concentration is 50% by weight, ^{the viscosity at 25 ° C. and a shear rate of 100s-1} is 400 mPa · s-10000 mPa · s, so that the slurry composition is thickened and the current collector foil Adhesion with and between molecules is improved. As a result, the thickener has an advantage that it is not necessary to use a dispersant or the like.

The negative electrode of a lithium ion secondary battery according to still another aspect of the present invention is characterized in that a mixed layer containing at least the slurry composition for a lithium ion secondary battery electrode is bonded to a current collector. ..

Further, the lithium ion secondary battery according to still another aspect of the present invention is characterized by including the above-mentioned lithium ion secondary battery negative electrode, a positive electrode, and an electrolytic solution.

According to the present invention, it is possible to obtain a slurry composition for a lithium ion secondary battery electrode having excellent binding properties, and further, it is possible to improve the battery characteristics of the lithium ion secondary electrode by using the slurry composition. ..

Hereinafter, embodiments of the present invention will be described in detail, but the present invention is not limited thereto.

The slurry composition for a lithium ion secondary battery electrode of the present embodiment is a binder composition containing a neutralizing salt of an α-olefin-maleic acid copolymer obtained by copolymerizing an α-olefin and a maleic acid, and a conductive support. It is composed of an agent, a negative electrode active material, and water, and has a viscosity of 400 mPa · s to 10,000 mPa · s at ^{25 ° C. and a shear rate of 100 s-1 when the solid content concentration is 50% by weight.}

In the present embodiment, the α-olefin-maleic acid copolymer obtained by copolymerizing an α-olefin and a maleic acid is composed of a unit (A) based on the α-olefin and a unit (B) based on the maleic acid. It is preferable that each component (A) and (B) satisfies (A) / (B) = 1/1 to 1/3 (molar ratio). Further, it is preferably a linear random copolymer having a weight average molecular weight of 10,000 to 500,000.

In the present embodiment, the unit (A) based on α-olefins is the general formula −CH ₂ CR ¹ R ² − (in the formula, R ¹ and R ² may be the same or different from each other, and hydrogen. , Representing an alkyl group or an alkenyl group having 1 to 10 carbon atoms). The α-olefin used in the present embodiment is a linear or branched olefin having a carbon-carbon unsaturated double bond at the α-position. In particular, an olefin having 2 to 12 carbon atoms, particularly 2 to 8 carbon atoms is preferable. Typical examples that can be used are ethylene, propylene, n-butylene, isobutylene, n-pentene, isoprene, 2-methyl-1-butene, 3-methyl-1-butene, n-hexene, 2-methyl-. 1-pentene, 3-methyl-1-pentene, 4-methyl-1-pentene, 2-ethyl-1-butene, 1,3-pentadiene, 1,3-hexadiene, 2,3-dimethylbutadiene, 2,5 −Pentadiene, 1,4-hexadiene, 2,2,4-trimethyl-1-pentene and the like can be mentioned. Of these, isobutylene is particularly preferable from the viewpoint of availability, heavy synthesis, and product stability. Here, isobutylene also includes a mixture containing isobutylene as a main component, for example, a BB fraction (C4 fraction). These olefins may be used alone or in combination of two or more.

In the present embodiment, as the unit (B) based on maleic acids, maleic anhydride, maleic acid, maleic acid monoester (for example, methyl maleate, ethyl maleate, propyl maleate, phenyl maleate, etc.), maleic acid, etc. Maleic anhydride derivatives such as diesters (eg, dimethyl maleate, diethyl maleate, dipropyl maleate, diphenyl maleate, etc.), imide maleate or N-substituted derivatives thereof (eg, imide maleate, N-methylmaleimide, N) N-substituted alkyl maleimides such as -ethylmaleimide, N-propylmaleimide, Nn-butylmaleimide, Nt-butylmaleimide, N-cyclohexylmaleimide N-phenylmaleimide, N-methylphenylmaleimide, N-ethyl N-substituted alkylphenylmaleimides such as phenylmaleimide, or N-substituted alkoxyphenylmaleimides such as N-methoxyphenylmaleimide, N-ethoxyphenylmaleimide, and halides thereof (eg, N-c). Lolfenylmaleimide), citraconic anhydride, citraconic acid, citraconic acid monoester (eg, methyl citraconate, ethyl citraconate, propyl citraconate, phenyl citraconate, etc.), citraconic acid diester (eg, dimethyl citraconate, diethyl citraconate, etc.) , Dipropyl citraconate, diphenyl citraconate, etc.), citraconic acidimide or N-substituted derivatives thereof (eg, citraconateimide, 2-methyl-N-methylmaleimide, 2-methyl-N-ethylmaleimide) , 2-Methyl-N-propylmaleimide, 2-methyl-Nn-butylmaleimide, 2-methyl-N-t-butylmaleimide, 2-methyl-N-cyclohexylmaleimide and other N-substituted alkylmaleimide 2-methyl 2-Methyl-N-substituted alkylphenylmaleimide such as -N-phenylmaleimide, 2-methyl-N-methylphenylmaleimide, 2-methyl-N-ethylphenylmaleimide, or 2-methyl-N-methoxy 2-Methyl-N-substituted alkoxyphenylmaleimides such as phenylmaleimide, 2-methyl-N-ethoxyphenylmaleimide), as well as these halides (eg 2-methyl-N-chlorophenylmaleimide) Preferred. Among these, maleic anhydride is preferably used from the viewpoint of availability, polymerization rate, and ease of molecular weight adjustment. Further, these maleic acids may be used alone or in combination of two or more.

The content ratio of each of the above structural units in the copolymer of the present embodiment is preferably in the range of 1/1 to 1/3 in terms of molar ratio of (A) / (B). This is because the advantages of hydrophilicity as a high molecular weight substance that dissolves in water, water solubility, and affinity for metals and ions can be obtained. In particular, it is desirable that the molar ratio of (A) / (B) is 1/1 or a value close to it, and in that case, the unit based on α-olefin, that is, the unit represented by -CH2CR1R2- and the unit. It is a copolymer having a structure in which units based on maleic acids are alternately repeated.

The mixing ratio of α-olefins and maleic acids for obtaining the copolymer of the present embodiment varies depending on the composition of the target copolymer, but is 1 to 3 times the number of moles of maleic acids α-. It is effective to use an olefin to increase the reaction rate of maleic acids.

The method for producing the copolymer of the present embodiment is not particularly limited, and for example, the copolymer can be obtained by radical polymerization. At that time, as the polymerization catalyst used, azo catalysts such as azobisisobutyronitrile and 1,1-azobiscyclohexane-1-carbonitrile, and organic peroxide catalysts such as benzoylpoxide and dicumylper oxide are used. preferable. The amount of the polymerization catalyst used needs to be in the range of 0.1 to 5 mol% with respect to maleic acids, but is preferably 0.5 to 3 mol%. As a method for adding the polymerization catalyst and the monomer, they may be added all at once at the initial stage of polymerization, but a method of sequentially adding them as the polymerization progresses is preferable.

In the method for producing a copolymer of the present embodiment, the molecular weight can be appropriately adjusted mainly by the monomer concentration, the amount of catalyst used, and the polymerization temperature. For example, as substances that reduce the molecular weight, salts of metals of Group I, II or III of the Periodic Table, hydroxides, halides of metals of Group IV, general formulas N≡, HN =, H ₂ N- or H. ₄ It is also possible to adjust the molecular weight of the copolymer by adding amines represented by N-, nitrogen compounds such as ammonium acetate and urea, mercaptans and the like at the initial stage of polymerization or during the progress of polymerization. The polymerization temperature is preferably 40 ° C. to 150 ° C., and more preferably 60 ° C. to 120 ° C. If the polymerization temperature is too high, the produced copolymer tends to be in the form of blocks, and the polymerization pressure may become extremely high. The polymerization time is usually preferably about 1 to 24 hours, more preferably 2 to 10 hours. The amount of the polymerization solvent used is preferably adjusted so that the obtained copolymer concentration is 5 to 40% by weight, more preferably 10 to 30% by weight.

As described above, the copolymer of the present embodiment usually preferably has a weight average molecular weight of 10,000 to 500,000. A more preferable weight average molecular weight is 15,000 to 450,000. When the weight average molecular weight of the copolymer of the present embodiment is less than 10,000, the crystallinity is high and the adhesive strength between particles may be reduced. On the other hand, if it exceeds 500,000, the solubility in water or a solvent becomes small, and it may be easily precipitated.

The weight average molecular weight of the copolymer of this embodiment can be measured by, for example, a light scattering method or a viscosity method. When the ultimate viscosity ([η]) in dimethylformamide is measured by using the viscosity method, the copolymer of the present embodiment preferably has an intrinsic viscosity in the range of 0.05 to 1.5. The copolymer of the present embodiment is usually obtained in the form of a powder having about 16 to 60 meshes of grains.

In the present embodiment, the neutralized salt of the copolymer is one in which active hydrogen of carbonyl acid produced from maleic acids reacts with a basic substance to form a salt and become a neutralized product. Is preferable. In the neutralized product of the α-olefin-maleic acid copolymer used in the present embodiment, the basic substance containing a monovalent metal and / or ammonia is used as the basic substance from the viewpoint of binding property as a binder. It is preferable to use.

The degree of neutralization is not particularly limited, but when used as a binder, it is usually 0.5 to 0.5 to 1 mol of carboxylic acid produced from maleic acids in consideration of reactivity with an electrolytic solution. It is preferably in the range of 1 mol, more preferably in the range of 0.6 to 1 mol, and it is desirable to use a neutralized one. With such a degree of neutralization, there is an advantage that the acidity is low and decomposition of the electrolytic solution is suppressed.

In the present embodiment, the degree of neutralization can be adjusted by a base, an infrared spectrum, an NMR spectrum, or the like, but in order to measure the neutralization point easily and accurately, titration by a base may be performed. preferable. The specific titration method is not particularly limited, but it is dissolved in water with few impurities such as ion-exchanged water and is prepared with a basic substance such as lithium hydroxide, sodium hydroxide and potassium hydroxide. It can be carried out by neutralizing. The neutralization point indicator is not particularly limited, but an indicator such as phenolphthalein, which indicates the pH by a base, can be used.

In the present embodiment, the amount of the basic substance containing a monovalent metal and / or ammonia used is not particularly limited and is appropriately selected depending on the purpose of use and the like, but is usually in a maleic acid copolymer. The amount is preferably 0.1 to 2 mol per 1 mol of maleic acid unit. The amount of the basic substance containing a monovalent metal is preferably 0.6 to 2.0 mol, more preferably 0.7 to 2. Mol, per 1 mol of the maleic acid unit in the maleic acid copolymer. When the amount is 0 mol, a water-soluble copolymer salt with little alkali residue can be obtained.

The reaction of the α-olefin-maleic acid copolymer with a basic substance containing a monovalent metal and / or ammonia can be carried out according to a conventional method, but is carried out in the presence of water, and the α-olefin-maleic acid is carried out. A method of obtaining a neutralized product of the copolymer as an aqueous solution is convenient and preferable.

Examples of the monovalent metal-containing basic substance that can be used in the present embodiment include hydroxides of alkali metals such as sodium hydroxide, potassium hydroxide, and lithium hydroxide; alkali metals such as sodium carbonate and potassium carbonate. Carbonates; Alkali metal acetates such as sodium acetate and potassium acetate; Alkali metal phosphates such as trisodium phosphate and the like. Of these, ammonia, lithium hydroxide, sodium hydroxide and potassium hydroxide are preferable. In particular, as the binder for the lithium ion secondary battery, it is preferable to use ammonia and lithium hydroxide. Basic substances containing monovalent metals and / or ammonia may be used alone or in combination of two or more. In addition, as long as it does not adversely affect the battery performance, a neutralized product of the α-olefin-maleic acid copolymer may be used in combination with a basic substance containing an alkali metal hydroxide such as sodium hydroxide. May be prepared.

Next, in the present embodiment, the pH of the aqueous solution containing 10% by weight of the binder composition is preferably 6 to 11. When the pH is less than 6, the solubility in water or a solvent becomes small and it easily precipitates, which makes slurry coating difficult. On the other hand, when the pH is higher than 11, the basic substance to be neutralized is excessively present in the mixed layer, so that it may become a resistance component.

The method for measuring the pH of the present embodiment is not particularly limited, and can be measured by an indicator method, a hydrogen electrode method, an antimony electrode method, a glass electrode method, a semiconductor sensor method, or the like. Among them, it is preferable to use the glass electrode method because the equilibrium time of the potential is fast and the reproducibility is good, the measurement can be performed on various solutions without being affected by the oxidizing agent and the reducing agent, and it is simple. ..

Next, in the present embodiment, the ring-opening rate of the copolymer represents the hydrolysis rate of the maleic anhydride moiety that polymerizes with the α-olefin when maleic anhydride is used as the maleic anhydride. In the copolymer of the present embodiment, the ring-opening rate is preferably 60 to 100%, more preferably 70% to 100%, and even more preferably 80 to 100%. If the ring-opening rate is too low, the degree of structural freedom of the copolymer is reduced and the elasticity is poor, so that the force for adhering the polar material particles to be adhered may be reduced, which is not preferable. Further, it may cause a problem that the affinity for water is low and the solubility is poor. The ring-opening rate can be determined by, for example, measuring the hydrogen at the α-position of the ring-opened maleic acid by 1H-NMR with reference to the hydrogen located at the α-position of maleic anhydride, or determining the ratio of the maleic acid. The ratio of the carbonyl group and the carbonyl group derived from the ring-opened maleic anhydride can also be determined by IR measurement.

Further, in the present embodiment, when the maleic anhydride is maleic anhydride, the neutralizing salt of the copolymer is a basic substance in which the active hydrogen of the carbonyl acid produced by the ring opening of the maleic anhydride is as described above. It reacts with and forms a salt to become a neutralized product. The degree of neutralization in this case is not particularly limited, but when used as a binder, in consideration of reactivity with the electrolytic solution, usually, with respect to 1 mol of carbonyl acid produced by ring opening, It is preferably in the range of 0.5 to 1 mol, more preferably in the range of 0.6 to 1 mol, and it is desirable to use a neutralized one. With such a degree of neutralization, there is an advantage that the acidity is low and decomposition of the electrolytic solution is suppressed. The degree of neutralization of the copolymer when maleic anhydride is used can be measured by the same method as described above.

The slurry composition for a lithium ion secondary battery electrode of the present embodiment (hereinafter, also simply referred to as an electrode slurry composition, a negative electrode slurry composition or a slurry composition) is the above-mentioned α-olefin-maleic acid copolymer. In addition, it further contains a conductive additive and water (solvent). The slurry composition is preferably used as a slurry for a negative electrode, but is not limited to that for a negative electrode.

Then, in the present embodiment, the viscosity of the slurry composition for electrodes is measured by a Brookfield type viscometer, and the viscosity of the slurry containing 50% by weight of solid content at 25 ° C. and a shear rate of 100s- ¹ is 400 mPa · s ~. It is 10000 mPa · s. Further, the viscosity is more preferably 500 mPa · s to 5000 mPa · s.
If the viscosity is less than 400 mPa · s, the coatability when the electrode is manufactured is poor, and it may not be possible to coat the electrode to the required thickness. Further, if the viscosity is higher than 10000 mPa · s, there is a possibility that the above-mentioned aqueous binder solution, conductive auxiliary agent (conductivity-imparting agent), negative electrode active material and solvent (water) cannot be mixed uniformly.

In the present embodiment, the viscosity of the slurry composition is determined by, for example, adjusting the molecular weight and the degree of neutralization of the copolymer, and / or the type, average particle size, particle shape, and particle size of the conductive auxiliary agent. It is possible, but not limited to, the above range by adjusting the type of electrode active material such as distribution, average particle size, particle shape, particle size distribution, and the like.

Further, in the present embodiment, the negative electrode of the lithium ion secondary battery is formed by binding a mixed layer containing at least the slurry composition for the negative electrode of the lithium ion secondary battery of the present embodiment and the negative electrode active material to the current collector. It is a feature. This negative electrode can be formed by applying the above-mentioned slurry composition for the negative electrode of a lithium ion secondary battery to a current collector and then removing the solvent by a method such as drying. If necessary, a thickener, a conductive auxiliary agent, or the like can be further added to the mixed layer.

In the slurry composition for the negative electrode of a lithium ion secondary battery, the amount of the neutralized salt of the α-olefin-maleic acid copolymer used with respect to 100 parts by weight of the negative electrode active material is usually 0.1 to 4 parts by weight. It is preferably 0.3 to 3 parts by weight, more preferably 0.5 to 2 parts by weight. If the amount of the copolymer is excessively small, the viscosity of the slurry for the negative electrode of the secondary battery may be too low and the thickness of the mixed layer may be thinned. Conversely, if the amount of the copolymer is excessively large, the discharge capacity may decrease. There is sex.

On the other hand, the amount of the solvent in the slurry composition for the negative electrode is usually preferably 40 to 150 parts by weight, more preferably 70 to 130 parts by weight, based on 100 parts by weight of the negative electrode active material.

Examples of the solvent in the negative electrode slurry composition of the present embodiment include water, methanol, ethanol, propanol, alcohols such as 2-propanol, cyclic ethers such as tetrahydrofuran and 1,4-dioxane, and N, N-dimethyl. Examples thereof include amides such as formiamide and N, N-dimethylacetamide, cyclic amides such as N-methylpyrrolidone and N-ethylpyrrolidone, and sulfoxides such as dimethyl sulfoxide. Of these, the use of water is preferable from the viewpoint of safety.

When water is used as the solvent of the slurry composition for the negative electrode of the present embodiment, the following organic solvent may be used in combination in a range of preferably 20% by weight or less of the whole solvent. As such an organic solvent, a solvent having a boiling point of 100 ° C. or higher and 300 ° C. or lower at normal pressure is preferable, and for example, hydrocarbons such as n-dodecane; alcohols such as 2-ethyl-1-hexanol and 1-nonanol. Esters such as γ-butyrolactone and methyl lactate; amides such as N-methylpyrrolidone, N, N-dimethylacetamide and dimethylformamide; organic dispersion media such as sulfoxide sulfones such as dimethyl sulfoxide and sulfolane.

Examples of the negative electrode active material (sometimes abbreviated as active material) added to the negative electrode slurry composition of the present embodiment include amorphous carbon, graphite, natural graphite, mesocarbon microbeads (MCMB), and pitch-based carbon. Carbonaceous materials such as fibers; Conductive polymers such as polyacene; Composite metal oxides represented by SiOx, SnOx, LiTIOx and other metal oxides, lithium metals, lithium-based metals such as lithium alloys; TiS ₂ , LiTiS Examples thereof include metal compounds such as _2.

Further, in order to more reliably bring the viscosity of the slurry composition of the present embodiment into a desired range, it is preferable that the average particle size of these negative electrode active materials is 1 to 30 μm.

In the present embodiment, a thickener can be further added to the negative electrode slurry composition, if necessary. The thickener to be added is not particularly limited, and various alcohols, particularly polyvinyl alcohol and its modified products, celluloses, and polysaccharides such as starch can be used.

The amount of the thickener to be added to the slurry composition for the negative electrode as needed is preferably 0.1 to 4 parts by weight, more preferably 0.3 to 3 parts by weight, based on 100 parts of the negative electrode active material. Parts, more preferably 0.5 to 2 parts by weight. If the amount of thickener is excessively small, the viscosity of the slurry for the negative electrode of the secondary battery may be too low and the thickness of the mixed layer may be thin. Conversely, if the amount of thickener is excessively large, the discharge capacity may decrease. ..

In addition, examples of the conductive auxiliary agent to be added to the slurry composition for the negative electrode of the present embodiment as needed include metal powder, conductive polymer, and acetylene black.

Further, in order to more reliably bring the viscosity of the slurry composition of the present embodiment into a desired range, it is preferable that the average particle size of these conductive auxiliaries is 25 to 60 nm.

In the present embodiment, the amount of the conductive auxiliary agent used is usually preferably 0.5 to 10 parts by weight, more preferably 1 to 7 parts by weight, based on 100 parts by weight of the negative electrode active material. Is desirable.

In the slurry composition of the present embodiment, the blending ratio of the binder composition: negative electrode active material: conductive auxiliary agent is usually about 0.5 to 10: 85 to 99.4: 0.1 to 5. preferable.

The current collector used for the negative electrode of the lithium ion secondary battery of the present embodiment is not particularly limited as long as it is made of a conductive material, and for example, iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, etc. Metallic materials such as gold and platinum can be used. One of these may be used alone, or two or more of them may be used in combination at any ratio.

In particular, when copper is used as the negative electrode, the effect of the slurry for the negative electrode of the lithium ion secondary battery of the present invention appears most. The shape of the current collector is not particularly limited, but it is usually preferably in the form of a sheet having a thickness of about 0.001 to 0.5 mm.

The method of applying the negative electrode slurry to the current collector is not particularly limited. For example, a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a dipping method, a brush coating method and the like can be mentioned. The amount to be applied is also not particularly limited, but the thickness of the mixed layer containing the active material, the conductive auxiliary agent, the binder and the thickener formed after removing the solvent or the dispersion medium by a method such as drying is 0.005 to 5 mm. The amount is preferably 0.01 to 2 mm, more preferably 0.01 to 2 mm.

The method for drying the solvent such as water contained in the slurry composition for the negative electrode is not particularly limited, and for example, aeration drying with warm air, hot air, and low humidity air; vacuum drying; irradiation ray drying with infrared rays, far infrared rays, electron beams, etc. Can be mentioned. The drying conditions should be adjusted so that the solvent can be removed as soon as possible while the speed range is such that the active material layer does not crack due to stress concentration or the active material layer does not peel off from the current collector. Further, it is effective to press the current collector after drying in order to increase the density of the active material of the electrode. Examples of the pressing method include a mold press and a roll press.

Further, the present invention also includes a lithium secondary battery provided with the above-mentioned lithium ion secondary battery negative electrode, positive electrode, and electrolytic solution.

In the present embodiment, as the positive electrode, a positive electrode usually used for a lithium ion secondary battery is used without particular limitation. For example, as the positive electrode active material, TiS ₂ , TiS ₃ , amorphous MoS ₃ , Cu ₂ V ₂ O ₃ , amorphous V ₂ O-P ₂ O ₅ , MoO ₃ , V ₂ O ₅ , V ₆ O Transition metal oxides such as ₁₃ and lithium-containing composite metal oxides such as _{LiCoO 2} , LiNiO ₂ , LiMnO ₂ and LiMn ₂ O _{4 are used.} Further, the positive electrode active material is prepared by using a conductive auxiliary agent similar to that of the negative electrode and a binder such as SBR, NBR, acrylic rubber, hydroxyethyl cellulose, carboxymethyl cellulose and polyvinylidene fluoride, and having a boiling point of 100 ° C. in water or the above normal pressure. A positive electrode slurry prepared by mixing with a solvent or the like at 300 ° C. or lower can be applied to a positive electrode current collector such as aluminum and dried to obtain a positive electrode.

Further, in the lithium ion secondary battery of the present embodiment, an electrolytic solution in which an electrolyte is dissolved in a solvent can be used. The electrolytic solution may be liquid or gel as long as it is used for a normal lithium ion secondary battery, and a battery that functions as a battery should be appropriately selected according to the type of the negative electrode active material and the positive electrode active material. Just do it. Specific electrolytes, for example, also known lithium salt is any conventionally _{available, LiClO 4, LiBF 6, LiPF} 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF 6, LiSbF 6, LiB 10 Cl 10 _{, LiAlC l4, LiCl, LiBr,} LiB (C 2 H 5) 4, CF 3 SO 3 Li, CH 3 SO 3 Li, LiCF 3 SO 3, LiC 4 F 9 SO 3, Li (CF 3 SO 2) 2 N , Lower aliphatic lithium carboxylate and the like.

The solvent for dissolving such an electrolyte (electrolyte solution solvent) is not particularly limited. Specific examples include carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate and diethyl carbonate; lactones such as γ-butyl lactone; trimethoxymethane, 1,2-dimethoxyethane, diethyl ether and 2-ethoxyethane. , Ethers such as tetrahydrofuran, 2-methyltetraxide; sulfoxides such as dimethylsulfoxide; oxolanes such as 1,3-dioxolane, 4-methyl-1,3-dioxolane; nitrogen-containing compounds such as acetonitrile and nitromethane; formic acid Organic acid esters such as methyl, methyl acetate, ethyl acetate, butyl acetate, methyl propionate, ethyl propionate; inorganic acid esters such as triethyl phosphate, dimethyl carbonate, diethyl carbonate; Oxazolidinones such as 3-methyl-2-oxazolidinone; sulton compounds such as 1,3-propane sulton, 1,4-butane sulton, and nafta sulton can be mentioned, and these can be used alone or in combination of two or more. When a gel-like electrolytic solution is used, a nitrile-based polymer, an acrylic-based polymer, a fluorine-based polymer, an alkylene oxide-based polymer, or the like can be added as a gelling agent.

The method for manufacturing the lithium ion secondary battery of the present embodiment is not particularly limited, and examples thereof include the following manufacturing method. That is, the negative electrode and the positive electrode are overlapped with each other via a separator such as a polypropylene porous membrane, wound or folded according to the shape of the battery, put into a battery container, and an electrolytic solution is injected to seal the battery. The shape of the battery may be any of known coin type, button type, sheet type, cylindrical type, square type, flat type and the like.

The lithium ion secondary battery of the present embodiment is a battery that has both adhesiveness and improved battery characteristics, and is useful in various applications. For example, it is very useful as a battery used in a mobile terminal that requires miniaturization, thinning, weight reduction, and high performance.

Examples of the present invention will be described below, but the present invention is not limited thereto.

(Example 1)
<Slurry composition for negative electrode>
As the slurry composition for the negative electrode, 96 parts by weight of natural graphite (DMGS, BYD, average particle size 16.5 μm) as the active material for the negative electrode, and a lithium-modified isobutene-maleic anhydride copolymer resin (maleic anhydride) as the binder composition. Super-P (manufactured by Timcal Co., Ltd., average particle size) containing 3 parts by weight of a 10 w% aqueous solution having an average molecular weight of 325,000, a degree of neutralization of 1.0, and a ring opening rate of 100% as a solid content and carbon black as a conductive auxiliary agent. 1 part by weight of solid content (40 nm) was put into a special container, and kneaded using a planetary stirrer (ARE-250, manufactured by Shinky). In order to adjust the viscosity of the slurry, water was added during kneading and the slurry was kneaded again to prepare a slurry for electrode coating having a solid content concentration of 50% by weight. The composition ratio of the active material and the binder in the slurry is graphite powder (negative electrode active material): conductive auxiliary agent: binder composition = 96: 1: 3 as a solid content.

<Manufacturing of negative electrode for batteries>
The obtained slurry composition is coated on a copper foil (CST8G, manufactured by Fukuda Metal Foil Powder Industry) of a current collector using a bar coater (T101, manufactured by Matsuo Sangyo Co., Ltd.), and a hot air dryer at 80 ° C. for 30 minutes. After primary drying at (manufactured by Yamato Kagaku), rolling processing was performed using a roll press (manufactured by Hosen). Then, after punching as a battery electrode (φ14 mm), an electrode for a coin battery was produced by secondary drying at 120 ° C. for 3 hours under reduced pressure conditions.

<Measurement of viscosity of slurry composition for negative electrode>
The slurry obtained above was measured at 25 ° C. with a Brookfield viscometer (manufactured by DV-I PRIME Brookfield). The viscosity at a shear rate of 100s- ¹ was 706 mPa · s.

<Measurement of negative electrode thickness for batteries>
The weight and thickness of the battery coating electrode obtained above (active material layer thickness of about 50 μm, active material weight of about 12 mg) were measured. A constant pressure thickness measuring device (manufactured by TECLOCK) was used for the thickness measurement, and the measurement was performed on 4 electrodes at 3 points each, and the result was 48 ± 0.3 μm.

<Electrode coatability>
Regarding the electrode coatability, the variation in the electrode film thickness was used as an index, and four electrodes were measured at three points each. Then, if the variation with respect to the average film thickness is 0 to ± 0.5 μm, it is ⊚, if it is ± 0.5 to ± 1.0 μm, it is ○, and if it is ± 1.0 to ± 2.0 μm, it is Δ, ±. If it was 2.0 μm or more, it was evaluated as ×. The results are shown in Table 1 below.

<Battery production>
The battery coating electrode obtained above was transferred to a glove box (manufactured by Miwa Seisakusho) in an argon gas atmosphere. A metallic lithium foil (thickness 0.2 mm, φ15 mm) was used for the positive electrode. In addition, a polyprofylene system (Celgard # 2400, manufactured by Polypore) was used as a separator, and the electrolytic solution was a mixed solvent system in which ethyl methyl carbonate was added to ethylene carbonate and diethyl carbonate of _{lithium hexafluorophosphate (LiPF 6).} 1M-LiPF6, EC / EMC = 3/7 vol%, VC 2 wt%) was used for injection to prepare a coin battery (2032 type).

<Evaluation method: Charge / discharge characteristic test>
The produced coin battery was subjected to a charge / discharge test using a commercially available charge / discharge tester (TOSCAT3100, manufactured by Toyo System). The coin battery is placed in a constant temperature bath at 25 ° C., and the battery is ^{charged with a constant current of 0.1 C (about 0.5 mA / cm 2} ) with respect to the amount of active material until it reaches 0 V with respect to the lithium potential, and further the lithium potential is charged. A constant voltage charge of 0 V was carried out up to a current of 0.02 mA. The capacity at this time was defined as the charging capacity (mAh / g). Next, a constant current discharge of 0.1 C (about 0.5 mA / cm ² ) was performed up to 1.5 V with respect to the lithium potential, and the capacity at this time was defined as the discharge capacity (mAh / g). The difference between the initial discharge capacity and the charge capacity was defined as the irreversible capacity, and the percentage of the discharge capacity / charge capacity was defined as the charge / discharge efficiency. For the DC resistance of the coin battery, the resistance value after one charge (fully charged state) was adopted. The above results are shown in Table 1 below.

(Example 2)
In the preparation of the slurry composition for the negative electrode, the composition ratio of the active material and the binder in the slurry was set to solid content, and graphite powder (negative electrode active material): conductive auxiliary agent: binder composition = 93: 1: 6. Except for the above, the same procedure as in Example 1 was carried out.
Then, when the viscosity of the slurry composition was measured by the same method as in Example 1, it was 3393 mPa · s.
Next, a coated negative electrode was produced by the same method as in Example 1, a coin battery was obtained, and a charge / discharge characteristic test was performed. The film thickness measured by the same method as in Example 1 was 47 ± 0.5 μm. The results are shown in Table 1 below.

(Example 3)
In the preparation of the slurry composition for the negative electrode, the composition ratio of the active material and the binder in the slurry was set to solid content, and graphite powder (negative electrode active material): conductive auxiliary agent: binder composition = 90: 1: 9. Except for the above, the same procedure as in Example 1 was carried out.
Then, when the viscosity of the slurry composition was measured by the same method as in Example 1, it was 8860 mPa · s.
Next, a coated negative electrode was produced by the same method as in Example 1, a coin battery was obtained, and a charge / discharge characteristic test was performed. The film thickness measured by the same method as in Example 1 was 47 ± 1.1 μm. The results are shown in Table 1 below.

(Comparative Example 1)
The slurry composition was the same as in Example 1 except that an isobutylene-maleic anhydride copolymer resin (average molecular weight 6,000, neutralization degree 1.0, ring-opening rate 100%) was used as the binder composition for the negative electrode. I made a thing.
Then, when the viscosity of the slurry composition was measured by the same method as in Example 1, it was 342 mPa · s.
Next, a coated negative electrode was produced by the same method as in Example 1, a coin battery was obtained, and a charge / discharge characteristic test was performed. The film thickness measured by the same method as in Example 1 was 52 ± 3.5 μm. The results are shown in Table 1 below.

(Comparative Example 2)
An isobutene-maleic anhydride copolymer resin (average molecular weight 650,000, neutralization degree 1.0, ring-opening rate 100%) was used as the binder composition for the negative electrode, and the slurry was prepared in the same manner as in Example 1 above. When a composition was prepared and an attempt was made to measure the viscosity by the same method as in Example 1, the viscosity was too high to be measured. Further, an attempt was made to prepare the mixed layer for the negative electrode by the same method as in Example 1, but the electrode coating could not be performed because the viscosity was so high that the mixed layer could not be uniformly mixed.

(Discussion)
The slurry compositions of Examples 1 to 3 having a viscosity in a predetermined range showed excellent coatability without adding a thickener, and it was easy to form a negative electrode. Then, as is clear from Table 1, it was shown that the batteries of Examples 1 to 3 realized low resistance.

On the other hand, in Comparative Example 1 using a low-viscosity slurry, the coatability was poor and the resistance was high because the solubility was low. On the other hand, in Comparative Example 2 using a high-viscosity slurry, it was difficult to knead the uniform slurry, and the slurry and the electrode could not be prepared.

Claims (3)

A lithium ion secondary battery electrode composed of a binder composition containing a neutralizing salt of an α-olefin-maleic acid copolymer obtained by copolymerizing an α-olefin and a maleic acid, a conductive auxiliary agent, a negative electrode active material, and water. Slurry composition for
The slurry viscosity measured under the following conditions is 400 mPa · s-10000 mPa · s.
A slurry composition for a lithium ion secondary battery electrode, wherein the α-olefin-maleic acid copolymer is an isobutylene-maleic anhydride copolymer.
<Measurement conditions >
Solid content concentration 50wt%
Solvent water measurement temperature 25 ° C
Slip speed 100s ^-1 A negative electrode of a lithium ion secondary battery formed by binding a mixed layer containing the slurry composition according to claim 1 to a current collector. The lithium ion secondary battery having the negative electrode of the lithium ion secondary battery according to claim 2.